As an apparatus for the head lamps of an automobile, a light distribution controller adopting ADB (adaptive driving beam) control is available in which glare to the driver of a preceding vehicle or an oncoming vehicle ahead of the subject vehicle is prevented and the visibility of the driver of the subject vehicle is enhanced. With this ADB control, when light irradiation is performed using high-beam light distribution, a vehicle ahead of the subject vehicle, such as a preceding vehicle or an oncoming vehicle, is detected, and light is shielded in a region where glare may be given to the driver of the detected vehicle ahead. That is, the region ahead of the subject vehicle is irradiated widely as much as possible while glare to the driver of the vehicle ahead is prevented and the visibility of the driver of the subject vehicle is improved. For example, according to Japanese Patent Document JP-A-2010-000957, a vehicle present ahead of the subject vehicle is detected, light distribution having additional light distribution in a region above a cut-off line of the low-beam light distribution pattern of the head lamps of the subject vehicle is formed, and this light distribution pattern is swivel-controlled in the left-right direction in response to the position of the vehicle ahead, whereby the visibility of the driver of the subject vehicle in the region ahead of the subject vehicle is improved without causing glare to the driver of the vehicle ahead.
With the ADB control described above, light distribution is switched primarily on the basis of the position of a vehicle ahead regardless of the type of the vehicle, that is, regardless of whether the vehicle is a preceding vehicle or an oncoming vehicle. As a result, when the position of the vehicle ahead changes frequently, the light distribution is switched frequently. This switching of the light distribution can disturb the driver of the subject vehicle. For example, when the ADB control for switching a light distribution pattern to a high-beam light distribution pattern having a different cut-off line shape is performed with an oncoming vehicle (in which the oncoming vehicle and the subject vehicle are supposed to pass each other), the oncoming vehicle moves from a region far ahead of the subject vehicle to a region closer to the subject vehicle. The light distribution pattern then is switched to a high-beam light distribution pattern, the cut-off line of which is displaced gradually rightward as the oncoming vehicle comes closer to the subject vehicle on a left-hand traffic road. For this reason, it is assumed that the pattern is switched to a light distribution pattern having a different cut-off line each time the subject vehicle and an oncoming vehicle pass each other. Accordingly, when the subject vehicle and multiple oncoming vehicles pass each other continuously, the light distribution pattern is switched repeatedly and frequently. This frequent switching of the light distribution pattern can disturb the driver of the subject vehicle.
Furthermore, ADB control has been proposed, where the ADB control is capable of performing the so-called swivel control, in which a light distribution pattern is moved in the left-right direction in response to the change in the position of a vehicle ahead. However, in this kind of ADB control, the driver of the subject vehicle can experience significant trouble when the subject vehicle and multiple oncoming vehicles pass each other. More specifically, when the subject vehicle and the leading oncoming vehicle pass each other and when the cut-off line of the light distribution pattern is moved rightward in response to the movement of the oncoming vehicle, the subsequent oncoming vehicle present far ahead is detected at a position close to the center of the pattern. Hence, the light distribution pattern is moved leftward instantaneously to respond to the position of the subsequent oncoming vehicle. In other words, the cut-off line of the light distribution pattern is controlled so as to move left to right and then right to left each time the subject vehicle and each oncoming vehicle pass each other. As a result, the light distribution pattern is moved frequently when the subject vehicle and multiple oncoming vehicles pass each other. This switching of the light distribution pattern can disturb the driver of the subject vehicle.